The present invention relates to personal computers, and in particular to a universal serial bus transceiver.
A standard has been developed for a universal serial bus (USB) for personal computers. According to this standard, set forth most recently in Universal Serial Bus Specification Revision 1.1, a universal serial bus transceiver provides logic signals on the bus at a signal level of five volts. In order to achieve this required bus signal level, the transceiver""s internal data lines must support voltages as high as 3.8 V.
The transceiver is typically integrated on the same chip with a USB controller. Thus, since smaller chip designs are not capable of handling larger voltages, the required internal transceiver voltage place a practical lower limit of approximately 0.5 microns on the design rule for the USB transceiver and controller. This lower limit severely restricts the ability of chip designers to either increase the functionality or reduce the chip size of the USB transceiver and controller. In addition, portable devices such as personal data assistants, palmtop computers and cellular telephones typically have lower system voltages which cannot easily support the required USB voltages.
Therefore, a need has arisen for a universal serial bus communication system that addresses the disadvantages and deficiencies of the prior art. In particular, a need has arisen for a universal serial bus communication system with separate controller and transceiver chips, to allow lower system voltage on the transceiver chip.
Accordingly, a novel universal serial bus transceiver is disclosed. In one embodiment, the transceiver includes a differential transmitting amplifier with a first input terminal that receives a reference voltage, a second input terminal that receives a first data input signal at a level corresponding to the reference voltage, and a third input terminal that receives a second data input signal at the level corresponding to the reference voltage. The differential transmitting amplifier generates first and second bus data output signal at the bus signal level in response to the first and second data input signals. The transceiver also includes a first receiving amplifier with a first input terminal that receives the reference voltage and a second input terminal that receives a first bus data input signal at the bus signal level. The first receiving amplifier generates a first data output signal at the level corresponding to the reference voltage. Similarly, the transceiver includes a second receiving amplifier with a first input terminal that receives the reference voltage and a second input terminal that receives a second bus data input signal at the bus signal level. The second receiving amplifier generates a second data output signal at the level corresponding to the reference voltage.
In another embodiment of the present invention, a USB-compatible electronic device includes a processor that generates data for transmission on a universal serial bus. The device also includes a universal serial bus controller, residing on a first integrated circuit chip, that receives the data for transmission on the universal serial bus from the processor and provides both a reference voltage and first and second data signals at a signal level associated with the reference voltage in response to the data received from the processor. The device also includes a universal serial bus transceiver, residing on a second integrated circuit chip, that receives the reference voltage and the first and second data signals from the universal serial bus controller and generates, in response to the first and second data signals received from the universal serial bus controller, first and second bus data output signals at a bus signal level that is different from the signal level associated with the reference voltage.
According to still another embodiment of the present invention, a method for communicating data via a universal serial bus includes receiving a controller reference voltage at a differential transmitting amplifier, receiving first and second controller data input signals at a level corresponding to the controller reference voltage at the differential transmitting amplifier, generating first and second bus data output signals at a bus signal level by the differential transmitting amplifier in response to the first and second controller data input signals, the bus signal level being different from the level corresponding to the controller reference voltage, and transmitting the first and second bus data output signals on the universal serial bus.
An advantage of the present invention is that the USB controller and USB transceiver may reside on separate integrated circuit chips, eliminating the need for the USB controller to support the universal serial bus signal level. Another advantage of the present invention is that the USB transceiver may be powered entirely by the universal serial bus voltage, eliminating the need for the power supply for the USB transceiver. Yet another advantage is that the disclosed generic USB transceiver is compatible with a variety of USB controllers utilizing different internal signal levels.